Complexity Explained is great site describing complexity science and complex systems. It walks visitors through categories such as Emergence and Dynamics using interactive visuals by Dirk Brockmann. Led by Manilo De Domenico and Hiroki Sayama with the support of several contributors.
Complexity Explorables created by Dirk Brockmann uses various collections of interactive simulations which model systems in areas such as biology, physics, and network science. Most of the visualizations were created using D3 (Data Driven Documents).